"We consider that we are bound by authority, which also accords with sound legal principle and policy, to hold that, before a written contract may be rectified on the basis of a common mistake, it is necessary to show either (1) that the document fails to give effect to a prior concluded contract or (2) that, when they executed the document, the parties had a common intention in respect of a particular matter which, by mistake, the document did not accurately record. In the latter case it is necessary to show not only that each party to the contract had the same actual intention with regard to the relevant matter, but also that there was an "outward expression of accord" – meaning that, as a result of communication between them, the parties understood each other to share that intention."
"27. First, the rules relating to rectification of a commercial contract assume that the parties have, in some sense, negotiated that contract. This point is made good in the passages that I have cited from Butlin's . Negotiation may take many forms, but the rationale of the authorities is that there will have been exchanges or discussions that lead to the written agreement in question. In this case, there were, on the trial judge's findings, no such exchanges or discussions, and more importantly there could not have been. Had the single solicitor acting for David and Dean known that they disagreed about how the beneficial interest in the property was to be divided, he would have been required by best professional practice to advise that separate representation was sought. 28. Secondly, and by way of a related but more general point, it must be relatively common for family members buying property jointly not to discuss openly how the beneficial interest is to be held. Plainly if the TR1 is signed by the transferees, such a discussion is more likely, but still not inevitable. 29. Thirdly, whilst the situation in this case is not at all the same as the situation in the pension scheme cases, which Leggatt LJ singled out for special treatment, it has features that distinguish it from a commercial context. Butlin's makes clear that different considerations will apply to settlements and declarations of trust. It may be that declarations of trust of the kind in issue in this case would also demonstrate special features. 30. Fourthly, the joint purchasers of properties hold the legal estate as trustees. Butlin's makes clear, at least, that the trustees' intentions may be relevant to rectification if they have themselves made a bargain. The bargain could mean that the beneficial interests would be held by persons other than or in addition to the trustees. In this case, for example, on one analysis David intended the property to be held for "his family"."
“On the face of the claim as it is brought by [the appellants] in this case, the transaction which is sought to be rectified was not simply a unilateral gift by [the mother] of her existing beneficial share in the Property since they claim that as part of the intended transaction [their late brother] was also to relinquish his existing share in the Property and they seek to give effect to this bargain by the rectification of the transfer. However, if they are unable to establish any common intention on the part of [their late brother] that he should relinquish his existing beneficial interest in the Property, that does not in my judgment preclude them from the lesser alternative claim for rectification of the transfer simply in relation to the disposal by Harbhajan of her beneficial interest in the Property if on the evidence there is convincing proof that [the mother] as donor of that interest intended to dispose of it to [the appellants] alone. In such a case it would not be necessary to show that [their late brother] or indeed [the appellants], shared in any common intention relating to the disposal of [the mother’s] interest, the claim instead depending upon what her subjective intention was and whether by a mistake that was not given effect to in the transfer.”